1. Field of the Invention
This invention relates to a novel method for the production of an organic acid and/or an organic acid ester. More particularly, this invention relates to a method for the production of an organic acid and/or an organic acid ester, with the thermal efficiency and consequently the operational efficiency thereof enhanced by effectively utilizing the large volume of heat generated in the process of production of an organic acid and/or an organic acid ester.
2. Description of the Related Art
Since large commercial plants such as chemical plants emit waste heat in large volumes, efforts have been devoted to make effective use of the waste heat to the fullest possible extent by introducing a technique for the utilization of heat.
The process for producing acrylic acid by the reaction of catalytic gas phase oxidation also emits waste heat in a large volume. Thus, efforts have been directed toward realizing effective use of the waste heat to the fullest possible extent by introducing a technique for the utilization of heat.
In performing this reaction of catalytic gas phase oxidation, since the raw material therefor must be supplied in a gaseous form, the liquefied propylene adopted as the raw material is gasified through a vaporizer and then supplied to a reactor. When the raw material is subjected to catalytic gas phase oxidation using a molecular oxygen-containing gas in the presence of a catalyst, a gaseous product which contains an organic acid aimed at by the reaction and by-products is obtained. The reaction generates the heat of reaction in a large volume at the same time. Generally, this heat of reaction is recovered by means of a heat exchanger. Meanwhile, the gas obtained by the catalytic gas phase oxidation is led to an organic acid absorbing column for the purpose of allowing the produced organic acid to be isolated, and exposed to an absorbing solvent (generally, water) so as to be cooled. And the organic acid and by-products are absorbed in the solvent. In a solvent separating column, this solution is deprived of the solvent contained therein. Then, in a purifying column, the resultant solution is distilled to separate the purified organic acid.
As regards the utilization of the heat of reaction that is generated when the organic acid is produced by means of the reaction of catalytic gas phase oxidation, JP-A-49-73381, for example, proposes a method for the recovery of the heat of reaction. This method of recovering the heat of reaction is embodied in the production of acrolein by the catalytic gas phase oxidation of propylene or the production of phthalic anhydride by the catalytic gas phase oxidation of ortho-xylene or naphthalene and is characterized by utilizing part of the heat of reaction generated for inducing generation of steam and superheating the produced steam with the remainder of the heat of reaction. According to this method, the heat of reaction generated by the reaction is utilized for the generation of steam and then utilized for the production of superheated steam. The superheated steam obtained is used as the source of motive power for a steam turbine which is connected to a compressor serving to supply air as the raw material for the reaction of catalytic gas phase oxidation. This method permits the heat of reaction to be recovered for reuse highly advantageously in terms of economy and operational efficiency.
The invention disclosed in the patent publication mentioned above, however, is a method for the recovery of the heat that emanates from the single-stage reaction of catalytic gas phase oxidation. When it is applied to an actual commercial-scale production plant, it occasionally requires promoting the reaction by disposing a plurality of reactors in series or in parallel and operating them so as to perform the necessary treatment in a series or parallel pattern. In this case, the method for the recovery of the heat of reaction mentioned above is required to be applied to each of the plurality of reactors. Therefore, the devices used for the recovery of the heat of reaction are required to be in such a quantity as to be commensurate with the number of reactors to be disposed. These requirements add to the cost of equipment and the measure for security and the measure for environmental protection which are brought about by the complication and exaction of the configuration of equipment. Thus, the invention has incurred the problem of augmenting the cost of design and development and the running cost as well.
The object of this invention is to provide a method for the production of an organic acid and/or an organic acid ester which comprises utilizing a steam system capable of constantly performing a reaction of catalytic gas phase oxidation without reference to the form of the reaction of an organic acid and capable of constantly realizing a high thermal efficiency for the waste heat generated in the process of production in any form of the reaction. As concrete examples of reaction of the organic acid, (1) one-stage reaction of catalytic gas phase oxidation or a multiple-stage reaction of catalytic gas phase oxidation; and (2) the mass production using a plurality of reactors disposed in a series or parallel arrangement and operated to perform the treatment in a series or parallel pattern or the treatment by the use of one reactor which is equipped with one or a plurality of chambers may be cited. Particularly the multiple-stage reaction of catalytic gas phase oxidation is implemented in various forms such as the treatment by using one or a plurality of reactors for each of the reactions and one reactor with intermediate tube sheets into a plurality of chambers and circulating a heat transfer media to each of the chambers independently so as to allow different reactions to proceed in the different chambers.
The present inventors have carried out diligent studies repeatedly. They have consequently found that, by recovering the heat generated at various places in the process for the production of an organic acid and/or an organic acid ester in the form of steam by a heat generating device and further using effectively the recovered steam at various places in the process for the production of an organic acid and/or an organic acid ester, it is made possible to perform stably the reaction of catalytic gas phase oxidation constantly and realize a steam system of constantly high thermal efficiency operated by the use of the waste heat generated in the process in any forms of reaction. The present inventors, regarding the system for controlling the device for the generation of steam and the steam line, have further found that, by controlling the pressure in the device and in the line independently, it is made possible to recover the energy retained by the generated heat more effectively in the form of steam throughout the whole process and use it stably even when the multiple-stage reaction of catalytic gas phase oxidation uses the heat transfer media at temperatures varied for the individual component reactions.
The method contemplated by this invention for the production of an organic acid and/or an organic acid ester is characterized by recovering the heat generated in the process for the production of an organic acid and/or an organic acid ester in the form of steam and using the steam formed in the process for the production of an organic acid and/or an organic acid ester in any forms of {circle around (1)} thermal energy, {circle around (2)} mechanical energy, and {circle around (3)} electric energy. When the method of this invention is used, the by-products and the discharged heat arising from the production plant can be utilized highly effectively as in simplifying the system and decreasing the quantity of the discharged steam. Particularly when (1) devices for generating steam and (2) steam lines for connecting the devices for generating steam to devices for consuming the steam are independently subjected to control of pressure with a view to recovering the heat in the form of steam and using the steam in a complex manner at various places in the process of production, the control can be implemented so that the steams of varying pressures individually obtained in the devices for generating steam may be individually supplied to the devices for consuming the steam under pressures proper therefor through the steam lines of varying pressures. Thus, the effects of the present invention can be augmented further.